A new approach to the identification of physiologically active peptides using covalent labeling techniques is in progress (using dansylation, reductive alkylation, and iodination). BIBLIOGRAPHIC REFERENCES: Gainer, H.: Peptides and neuronal function, In: Costa, E. (Ed.): Advances in Biochemical Psychopharmacology, Vol. 15, New York, Raven Press, 1976, pp. 193-210. Ifshin, M.S., Gainer, H. and Barker, J.L.: Peptide factor extracted from molluscan ganglia which induces bursting pacemaker activity. Nature 254: 72-74, 1976.